Studies of the action of epinephrine on carbohydrate metabolism of incubated rat diaphragm have shown that epinephrine markedly inhibits glucose metabolism in skeletal muscle. The decrease in glucose utilization is equal to the decrease in glycogen synthesis. Similar effects were found with phosphodiesterase (PDE) inhibitors. It was concluded that cyclic AMP in addition to stimulating glycogenolysis also specifically diminishes glycogen synthesis. Experiments have also been concerned with the action of hormones in uracil nucleotide metabolism in cardiac and skeletal muscle. Streptozotocin diabetes in rats led to a significant decrease in UTP content and uridine kinase activity in these tissues. Insulin treatment of the animals restored values to normal. Thyroid hormone also influences uracil nucleotide metabolism in heart and other tissues.